This invention relates to a method of and an apparatus for measuring a metal terminal crimped to a sheathed wire.
In the production of a wire-connected metal terminal, generally, a sheath is removed from an end portion of a sheathed wire, and then the metal terminal is crimped to an exposed portion of a core wire (conductor) and that portion of the sheath disposed adjacent to this exposed core wire portion.
The metal terminal includes two pairs of crimping piece portions, each pair of crimping piece portions extending upwardly respectively from opposite side edges of a base plate portion for the placing of the sheathed wire thereon. More specifically, there are provided the pair of sheath crimping piece portions to be press-fastened to the sheath and the pair of core wire crimping piece portions to be press-fastened to the core wire.
A crimping machine for crimping the metal terminal to the sheathed wire includes a die for press-deforming the crimping piece portions of the metal terminal. The die comprises an anvil for the placing of the base plate portion of the metal terminal thereon, and a crimper which cooperates with the anvil to press-deform the crimping piece portions of the metal terminal.
The metal terminal is pressed between the anvil and the crimper of the crimping machine, and is crimped to the sheathed wire in such a manner that the pair of sheath crimping piece portions are press-fastened to the sheath, while the pair of core wire crimping piece portions are press-fastened to the core wire.
After the metal terminal is crimped to the sheathed wire, a contact resistance between the core wire and the metal terminal and a force (strength) of clamping of the metal terminal to the sheathed wire are evaluated. These evaluations have heretofore been manually conducted for selected samples, using an ohm-meter and a tensile tester. However, there has now been proposed an automatic evaluation apparatus for measuring a resistance value and a tensile strength for all of wire-connected metal terminals (see, for example, JP-A-2000-207956).
Here, a height of a core wire crimping portion formed by the pair of core wire crimping piece portions press-fastened to the core wire is defined as its dimension in a direction perpendicular to the base plate portion, and it is known that this height is an important index related to the contact resistance between the core wire and the metal terminal and the force (strength) of clamping of the metal terminal to the sheathed wire.
In the automatic evaluation apparatus disclosed in JP-A-2000-207956, a resistance value, a tensile strength and a height of the core wire crimping portion are measured for each metal terminal, and the optimum height of the core wire crimping portion is determined from statistics of measured values so that the resistance and the tensile strength both can take proper values within the standard range, and the distance between an anvil and a crimper is automatically adjusted so that the core wire crimping portion can be formed into the proper height.
The metal terminal is crimped to the sheathed wire in such a manner that the pair of core wire crimping piece portions are press-fastened to the core wire and that the pair of sheath crimping piece portions are press-fastened to the sheath. Therefore, the clamping force of the metal terminal is obtained also by the pair of sheath crimping piece portions press-fastened to the sheath.
In the automatic evaluation apparatus disclosed in JP-A-2000-207956, only the height of the core wire crimping portion formed by the pair of core wire crimping piece portions press-fastened to the core wire is measured and evaluated, and the height of a sheath crimping portion formed by the pair of sheath crimping piece portions press-fastened to the sheath is not measured and evaluated.
In some cases, the pair of sheath crimping piece portions are press-fastened to the sheath in such a manner that one of these sheath crimping piece portion overlaps the other. In such a case, the resultant sheath crimping portion has a generally round cross-sectional shape, and a portion (measurement portion) of the sheath crimping portion to be measured can not be easily determined, and an overlapping portion and a non-overlapping portion adjacent thereto much differ in height from each other.
Therefore, for measuring and evaluating the height of the sheath crimping portion, it is necessary to establish standards for determining a measurement portion common to all of metal terminals to be subjected to measurement.